1. Field of the Invention
The present invention relates to an active matrix type semiconductor display device, and particularly to an active matrix type liquid crystal display device.
2. Description of the Related Art
In recent years, as an FPD (Flat Panel Display), an active matrix type semiconductor display device enlivens the market. Above all, an active matrix type liquid crystal display device has been frequently used as a display device of a personal computer. Further, in addition to a use for a note-sized personal computer, the active matrix type liquid crystal display device with a large screen comes to be used for a desktop personal computer.
For the active matrix type liquid crystal display device used for a personal computer, in addition to a request for a large screen, it is required that plural pieces of information can be displayed at the same time. Then, the active matrix type liquid crystal display device which has a large screen, high fineness, and high picture quality, and enables a full color display, has been required.
Among active matrix type liquid crystal display devices, a TN (twisted nematic) liquid crystal display device using a nematic liquid crystal appears most frequently on the market. FIG. 20 is a schematic structural view showing a conventional active matrix type TN liquid crystal display device. In FIG. 20, reference numeral 3001 designates a source signal line driver circuit; 3002, a gate signal line driver circuit; and 3003, an active matrix circuit. The active matrix circuit 3003 is a circuit in which a plurality of pixel TFTs 3004 are arranged in matrix form. A gate signal line and a source signal line are connected to a gate electrode and a source electrode of each of the pixel TFTs 3004, respectively. A pixel electrode is connected to a drain electrode of the pixel TFT. In general, a substrate having a driver circuit and an active matrix circuit is called an active matrix substrate. A liquid crystal 3006 is sandwiched between the active matrix substrate and a counter substrate (not shown) on the entire surface of which a counter electrode is formed.
A selection signal is sequentially supplied to the gate signal line from the gate signal line driver circuit. All pixel TFTs connected to the gate signal line to which the selection signal is supplied are turned ON, and the source signal line driver circuit 3001 sequentially supplies an image signal to the source signal line, so that writing of the image signal to the pixel TFT (that is, the liquid crystal and holding capacitance) is carried out.
In general, in the case where a material having hysteresis with respect to an applied voltage, such as a nematic liquid crystal, is used, an electric field in a reverse direction is applied to the liquid crystal at every predetermined period in order to prevent “burning” of a screen. This driving system is called an inversion driving system. The “hysteresis” with respect to the applied voltage means that the change in electrooptical characteristics of the liquid crystal when the voltage is applied does not coincide with the change in electrooptical characteristics of the liquid crystal when the voltage is removed. The “burning” of the screen means a disturbance of display which occurs due to this hysteresis.
For the purpose of preventing the above “burning” of the screen, a driving system called the inversion driving system is often used. In this inversion driving system, a system in which a direction of an electric field applied to a liquid crystal is inverted at every rewriting of a display screen is called a frame inversion system. This system is a driving system which can be easily carried out among the inversion driving systems. The frame inversion system is conventionally most frequently adopted for an active matrix type liquid crystal display device.
In recent years, while an active matrix type liquid crystal display device having high resolution/high fineness has been required, a problem of the frame inversion system becomes clear. For the purpose of realizing the active matrix type liquid crystal display device having high resolution/high fineness, it is necessary to shorten a period in which an image signal is charged in a liquid crystal and holding capacitance. From the performance of a driver circuit, there is a limit in shortening of this charging period, and a time division driving system has been newly adopted. However, in the case where a liquid crystal is driven by the frame inversion system, when the time division driving system is used, a so-called crosstalk phenomenon may occur, which deteriorates the quality of a display screen through parasitic capacitance which can not be avoided in design.
For the purpose of decreasing this crosstalk phenomenon, a gate line (row) inversion system which is such a system that a direction of an electric field applied to a liquid crystal is inverted for every image signals of one to several rows, or a source line (column) inversion system which is such a system that a direction of an electric field applied to a liquid crystal is inverted for every image signals of one to several columns, begins to be adopted.
The property of low power consumption is required especially for an active matrix type liquid crystal display device of a note-sized personal computer. However, even in the case where any of the foregoing three inversion driving systems is used, it is necessary to prepare a high potential side power source and a low potential side power source, and to prepare an image signal having a potential at a side of the high potential side power source and an image signal having a potential at a side of the low potential side power source. Thus, it becomes necessary to provide a difference between the high potential side power source and the low potential side power source in a driver circuit, which is approximately twice as large as that of the case where the inversion driving system is not used. As a result, such a state is caused that reliability of components such as TFTs making a driver circuit and an active matrix circuit is deteriorated, and consumed electric power of the driver circuit is increased. Besides, in the case where the high potential side power source of higher voltage is used for a part of the driver circuit, it becomes necessary to provide a booster circuit for conversion into a signal of higher voltage required for screen display, and as a result, there occurs a problem that an area of the driver circuit becomes large.